PROJECT ABSTRACT Non-alcoholic fatty liver disease (NAFLD) poses a major health risk to a growing sector of Americans. Non-alcoholic steatohepatitis (NASH) - a more aggressive liver lesion - along with NAFLD are the hepatic manifestations of metabolic syndrome (MetS), for which insulin resistance and inflammation are thought to be key drivers. This proposal takes advantage of mice with an intestinal permeability defect in tight junctions (TJs) of the intestinal epithelium that develops as a consequence of a targeted deletion of the junctional adhesion molecule A (JAM-A). Preliminary data, obtained from both JAM-A global knockout (JAM-A-/-) and VillinCreJAM- AFL/FL mouse colonies fed an obesogenic diet (HFCD), demonstrate robust steatohepatitis and early hepatic stellate cell ( H S C ) activation after eight weeks. These data raise critical unanswered questions regarding the molecular dysfunction associated with intestinal permeability and direct association with NASH progression. The proposed model will provide a unique opportunity to elucidate the molecular and cellular mechanisms responsible for impaired intestinal barrier function, significant lipopolysaccharide (LPS) translocation, as measured in vivo, that are conducive to development and progression of NASH. Therefore, the central hypothesis of this application is western diet-induced gut dysbiosis synergizes with impaired barrier function of VillinCreJAM-AFL/FL mice to facilitate translocation of LPS to the liver, promoting inflammation and fibrosis resulting in NASH progression. The central hypothesis will be tested by the following integrated specific aims. AIM 1: Demonstrate a direct link between gut LPS and hepatic innate immune activation that drives NASH development and progression in the setting of altered intestinal permeability. We hypothesize that hepatic TLR activation driven by gut LPS drives hepatic inflammation in HFCD-fed VillinCreJAM-AFL/FL mice. We will substantiate our hypothesis by determining whether treatment with an agent that can bind LPS, sevelamer, attenuates hepatic inflammation and fibrosis in HFCD-fed VillinCreJAM-AFL/FL mice. AIM 2: To test whether NASH development is dependent on a synergistic relationship between increased intestinal permeability in HFCD-fed VilllinCreJAM-AFL/FL mice and a HFCD-induced pro-inflammatory gut microbiota: We hypothesize that Western diet-induced gut microbial dysbiosis results in mucosal inflammation that further disrupts intestinal TJ molecular assembly and severely compromises gut barrier function. AIM 3: To verify that HFCD-fed VilllinCreJAM-AFL/FL mice have accelerated fibrosis as a consequence of impaired natural killer (NK) cell function that promotes hepatic stellate cell (HSC) survival. We hypothesize that HFCD-mediated depletion or functional impairment of NK cells promotes HSC survival in VillinCreJAM-AFL/FL mice. Given the preliminary data, proposed hypothesis and aims, this unique model of NASH will provide mechanistic insights that will have a high likelihood of clinical applicability for potential treatment for NASH.